Electric blasting initiator



Jan. 14, 1941. ENGUSH HAL 2,228,873

ELECTRIC BLAST ING INITIATOR Filed Aug. 30, 1939 ATTORNEY Patented Jan. 14,

PATENT m lee "2,228,873 ELECTRIC nmls'rmo INITIATOR Myrle Hardt English, Pompton Lakes, N. 1., and Roland Roswell Nydegger, Wilmington, Del, as-

signors to E. I. du Pont de Nemours & Company, Wilmington, Del a'corporation of Delaware Application August 30, 1939, Serial No. 292,590 .3 Claims. (Cl. 102-7) The present invention relates to the art of electric blasting initiators.

This application is a continuation-in-part of our copending application, Serial Number 181,647, 6 filed December 24,1937, and contains matter divided out of said copending application.

The electric blasting initiators known to the art have been characterized by several outstanding defects. They have not been completely im-' 1 pervious to water and/or moisture, especially under storage conditions and other rigorous conditions imposed in the field. Consequently these initiator structures of the prior art have not been' sufliciently durable to withstand the physical 35 wear encoui ltered in the field, including forces tending to pull the leg wires out of the cap, such. as severe tamping and the like. Furthermore their lack of resistance to abrasion, especially at the locus of the entrance of theleg wires into 0 the mouth or the shell, has been recognized as productive of many difllculties including short circuits, accidental firing, misflres, and the like.

' The object of the present invention is the pro-f .duction of a new and improved electric blasting initiator. A further object is an electric blasting initiator-so constructed that the leg wires are firmly gripped toresist forces which would otherwise tend to pull them out of the initiator. An additional object is an electric blasting initiator 0 of enhanced water resistance. Another object is such an initiator with improved abrasion resistonce at the locus of the emergence of the leg wires from the mouth of the shell.

We have determined that the foregoing objects are accomplished and disadvantages overcome the'inventlon, but should not be construed'to limit the scope thereof. Like numerals designate 50 corresponding parts throughout the several figures. I Referring generally to the various figures of 1 the drawing, Figure 1 is a view in cross-section of the improved electrlc'blasting initiator of our'in- 65 vention. Figure 2. is an enlarged view of the rubber-like plug formed about the leg wires bearing plastic insulation. Figure 3 is a'similar view wherein the plug takes a different form. Fig. 4

is a bottom end view of the modification shown 5 in Fig. 3.

Referring in greater detail to the various flgures, in Figure 1 the numeral I designates a metal shell into which the plug 2, formed about the leg wires 3, is crimped in water impervious relationship at 4. These leg wires 3 are provided with durable plastic insulation 5, preferably comprising an ethyl cellulose composition. This insulation preferably terminates within the body of the plug, as shown at locus 6. The rubber-like plug material is molded and/or vulcanized about both the exposed and insulated portions of the wires to form a. water impervious juncture at the interface between plug and insulation. This operation may be carried out by any molding process. We prefer to employ the pressure molding process described and claimed in our copending application, Serial Number 181,647, filed December 24. 1937, from which much of the subject matter of the present application was derived, pursuant to a requirement for division.

We have described our plug material as "rubber-like. By this term we refer to those properties generally possessed by natural and syn- I thetic rubber compositions and the like, namely,

elasticity, springiness, extensibility, and in one sense of the word, compressibility. This capacity of our plug material for rebounding, springing back and returning to its original shape without permanent deformation, which is characteristic of natural and synthetic rubber and similar compositions, is eifective in this electric blasting initiator of our invention for the purpose of forming a water impermeable closure between the shell positions comprising cellulose others generally.

and including toughening agents, conventional plasticising agents and the like, compositions comprising cellulose derivatives except nitrocellulose, compositions comprising, respectively,

polyvinyl acetals, methacrylic acid derivatives, polythene compositions, and similar durable plastic and/or thermoplastic materials. This material preferably is disposed about the conductor as a solid sheath, extruded sheaths being preferred.

The electric blasting initiator product of our invention possesses several outstanding advantages. The combination of the rubber-like plug molded about the thermoplastic insulation produces an electric blasting initiator of enhanced water resistance due to the effective juncture of the plug material with the insulation as a result of the vulcanizing and/or molding process in which the plug is formed. Furthermore, remarkably improved abrasion resistance results at the locus in which the leg wires emerge from the plug at the mouth of the shell, perhaps due to the slight, temporary give in the plug when pressure is exercised on the leg wires and due in particular to the effective seal between plug material and plastic insulation on said wires. Furthermore, because of the eifective seal of plug material to plastic insulation, the leg wires are firmly gripped in the shell to resist forces otherwise tending to pull them out of the initiator, such as those forces encountered in tamping operations and the like. This initiator completely solves the waterproofing problem for electric blasting initiators, a problem which has been a continual sourceof complaint for many years. In the conventional types when a column of waterproofing material was poured over the bridge plug and allowed to solidify within the cap shell, the results were never satisfactory. At summer temperatures the' material tended to soften, flow past the plug, and desensitize the cap charges. At very low temperatures, also, the seal was none too tight. In addition to the waterproofing composition it was necessary to superpose a sulfur composition. The rubber-like plug has eliminated these two-sealing compositions and has insured water tightness. Furthermore it permits the use of a considerably shorter cap shell. This is particularly desirable in the case of. delay initiators, where the length is very considerable in those of the higher delay periods.

Our assembly gives an improved waterproof coatings, and accordingly the initiator assembly will stand more abuse, generally, without impairment of function. Furthermore this insulation presents an improved appearance and allows ready diiierentiation between different types of electric wires and between the two leg wires by the use of variously colored pigments. For instance,

an assembly wherein insulation of one leg wire contains a yellow pigment and the insulation of the other contains a red pigment. However, any conceivable contrasting colors may be employed. This permits the miner or blaster to tell at a glance which wire he is dealing with at any point throughout itslength without tracing the same back to any. other point. This is especially advantageous in operations in which leg wires of unusual length are employed. We find that product to be especially desirable which is prepared by the process of our copending application, Serial Number 181,647, filed December 24, 1937. As a result of this process the plastic insulation is joined to the rubber-like plug in the step of vulcanizing the plug in place without impairment of the insulation at any point and without any harmful effect on the insulation from the vulcanizing heat, as disclosed and claimed in said copending application. This result is accomplished. by the step of maintaining the thermoferred embodiments of our invention. It will be loaded shell, spaced leg wires provided with insulation comprising a thermoplastic material entering the mouth of said shell, a plug of rubberloaded shell, the closure elements comprising leg 7 wires provided with insulation comprising a thermoplastic material, a plug of rubber-like material of the character described formed about said leg wires and in contact with said thermoplastic insulation substantially in the absence of the intermingling of said thermoplastic insulation with said rubber-like composition, said wires and plug being disposed in a position closing the mouth of said shell, and a cn'mp extending around the circumference of said shell in the region enclosing said plug forcing the shell wall into and deforming said rubber-like plug to complete a water impervious juncture.

MYRLE HARDT ENGLISH. ROLAND R. 

